The present invention relates to force sensors with elastic surface waves, particularly to those incorporating at least one oscillator connected to transducers located on one face of a mechanical part subjected to a force to be measured. It can be used especially in accelerometers and makes it possible to measure a component of the acceleration generating a force on the sensor.
There are known systems, such as those described in French Patent Applications Nos. 83/08,428 and 83/16,993 filed respectively on 20th May 1983 and 25th Oct. 1983 by the Applicant Company, and in these there are, on the surface of the sensor, transducers designed to excite and pick up elastic surface waves, the speed of propagation of which is known to vary as a function of the mechanical stresses in the direction of wave propogation. The sensor is therefore designed so that a force to be measured gives rise to a stress in the direction of wave propogation. To establish a direct known relation between the force to be measured and the stress, the sensor is oriented in such a way that the force to be measured forms a known angle with the direction of propagation of the elastic surface wave. For example, as regards the force sensor which is the subject of Patent Application No. 83/08,428, relating to a sensor with a flexible lamella, in which the stresses measured are bending stresses induced in the lamella, the force to be measured is exerted perpendicularly to the main plane of the lamella, where the bending stresses are detected.
As a result of this, to measure a force of unknown direction, it is necessary to provide means of detecting the direction of the force and of orienting the sensor in an appropriate way. For example, where an accelerometer is concerned, a ballast system associated with the sensor must be provided, to ensure that the effect of the acceleration is to put the sensor in the proper position and that the stress measured can be interpreted and give the acceleration value.
The vectorial force sensor according to the invention makes it possible to measure the three components of a force of unknown direction according to a specific trihedron, without having to orient the sensor, thereby making it possible to do without any balancing systems.